Calculating Cumulative elevation gain give me wierd results

问题

I have the app that use CoreLocation and track user movement.
When user is walking or driving I save each coordinate to local database (lat/lng/alt) so I can draw route based on saved coordinates.
A few days ago I have added Cumulative elevation gain and I use this code in

didLocationUpdate:
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    netElevationGain += MAX(0, oldLocation.altitude - newLocation.altitude);
}

But something is just wrong.
I started the application and start walking and walking around for a few miles and I get netElevationGain almost 500 meters. Which no way it's correct.
This is the list of netElevation saved in database for each point:

0,41,43,44,47,52,55,62,73,80,91,100,114,140,146,153,159,180,199,208,228,240,259,275,320,329,349,359,366,375,381,392,408,419,428,437,446,449,462,469,478,486

Altitudes
0.000000,181.678055,181.891495,182.786850,179.315399,177.035721,182.636307,181.259399,178.653015,192.552551,185.398819,182.693436,181.369766,154.306747,157.031693,159.748871,185.080856,198.080673,176.473877,178.646851,175.784424,178.184128,181.237488,188.956894,177.713181,193.673019,188.470184,182.749054,181.966507,181.547592,191.638657,198.713989,188.582977,197.977921,203.184540,205.108856,198.304123

To display gain I use simple select max(gain) from table where ...

UPDATE

Now I get worse values (in descending order):
Alt:

200.334869,200.594666,196.293945,195.240234,191.800446,192.622375,179.951385,179.185577,179.681122,177.843719,183.459595,174.170502,0.000000

gain:

307,301,294,285,275,269,252,246,234,227,217,202,0

回答1:

I took the values you've listed and ran them as follows:

NSArray *altitudes = @[ @(0.000000), @(181.678055), @(181.891495), @(182.786850), @(179.315399), 
                        @(177.035721), @(182.636307), @(181.259399), @(178.653015), @(192.552551), 
                        @(185.398819), @(182.693436), @(181.369766), @(154.306747), @(157.031693), 
                        @(159.748871), @(185.080856), @(198.080673), @(176.473877), @(178.646851), 
                        @(175.784424), @(178.184128), @(181.237488), @(188.956894), @(177.713181), 
                        @(193.673019), @(188.470184), @(182.749054), @(181.966507), @(181.547592), 
                        @(191.638657), @(198.713989), @(188.582977), @(197.977921), @(203.184540), 
                        @(205.108856), @(198.304123) ];

float netAlt = 0.0f;

// Start with the third value as we're only interesting in net gain
for (NSInteger i = 2; i < altitudes.count; i++) {
    float oldAlt = [altitudes[i-1] floatValue];
    float newAlt = [altitudes[i] floatValue];

    // newAlt - oldAlt because we're interested in the 
    // difference between current and previous
    float diff = newAlt - oldAlt;

    netAlt += MAX(0, diff);
    printf("%.0f,", netAlt);
}

This produced the following output:

0,1,1,1,7,7,7,21,21,21,21,21,23,26,51,64,64,67,67,69,72,80,80,96,96,96,96,96,106,113,113,122,127,129,129

This seems reasonable and realistic to me. It's not at all clear how how you managed to get the values you have. They make no sense.

来源：https://stackoverflow.com/questions/19210248/calculating-cumulative-elevation-gain-give-me-wierd-results

标签

ios

objective-c

core-location

cllocationmanager